Moq and DbSet without interfaces.

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C#

ASP.NET

Hello,

I have a problem with unit tests in work(I'm new in unit test world). I have to test Provider who operates on ApplicationDbContext and DbSets but there aren't any interfaces of that and they are not virtual members.
I can't create them becouse application is to big to make changes.

So, I need to work on classes. Now i have problem.

I need to test somethink like that:

public bool AddOrUpdateSomeDbSet(SomeClass doc)
       {
           this.db.SomeDbSet.AddOrUpdate(doc);

           try
           {
               this.db.SaveChanges();
               return true;
           }
           catch (Exception)
           {
               //TODO: logging
               return false;
           }
       }

So firsty I want to test a success try.
1. "db" is ApplicationDbContext.
2. I need to mock db.
3. db.SomeDbSet.AddOrUpdate(doc) must return some stuff to don't crash test.
4. db.SaveChanges() must return stuff too

And I have problem with point 3 and 4.

About point number 3:
I have somethink like that:

// That doesn't work because there is no .Return after that code. I dont know why.
contextMock.Setup(x => x.SomeDbSet.AddOrUpdate(It.IsAny<SomeClass>())).Returns(SomeStuff)

About point number 4:
In context are two methods SaveChanges() and SaveChanges(string value)

contextMock.Setup(x => x.SaveChanges("a")).Returns(1); // WORK
contextMock.Setup(x => x.SaveChanges()).Returns(1); // dont work
// An expression tree may not contain a call or invocation that uses optimal arguments - hmm? 

Can anyone help me with it?